Torque limiting threaded fastener

ABSTRACT

A torque limiting threaded fastener defined by a conventional nut or bolthead and a surrounding, geometrically similar driver resiliently interconnected with the normal torque applying faces of the conventional nut or bolthead.

0 United States Patent 1 1 1111 Means? Stone, Jr. 1 Jan. 9, 1973 [54]TORQUE LIMITING THREADED [56] References Cited FASTENER UNITED STATESPATENTS [76] Inventor: Wayne 13. Stone, Jr., 7307 Nevis 2,366,257 1/1945Hartley ..85/61 Road Bethesda 20034 3,289,524 12/1966 Rubin ..85/61Filed: P 10, 1970 Primary Examiner-Edward C. Allen [21] APPL NOJ 70,994Attorney-Wayne B. Stone, Jr.

[57] ABSTRACT A torque limiting threaded fastener defined by a con- U.S-

ventional nut or bolthead and a surrounding geomet- [51] lnt.Cl ..Fl6b31/02 rically similar driver resiliently interconnected with 58 Field ofSearch ..85/6l; 151/52; 81/524 the normal torque pp y faces of theconventional nut or bolthead.

7 Claims, 11 Drawing Figures PATENTEDJM 9 ma 3709.087

FIGI 24 24 P WAYNE B. STONE, JR.

INVENT OR ATTORNEY TORQUE LIMITING THREADED FASTENER BACKGROUND OF THEINVENTION Torque limiting wrenches are conventionally used to apply apredetermined torque to threaded fasteners. These wrenches arerelatively expensive and are not always available to manufacturers fieldpersonnel, small machine shops and home mechanics. Consequently, torquelimiting nuts are frequently used in original assembly operations wherethere is likelihood that the nuts may become loose in service andrequire tightening in the field. This is particularly common in theaircraft industry where many military and civilian specificationsrequire the use of torque limiting nuts for certain applications. Theiruse is more limited in other areas because of their substantial expense;it being more economical in the long run to purchase torque limitingwrenches.

Known torque limiting nuts require the fabrication of special threadedelements and clutching components which explains their substantialexpense. One typical nut of this type involves two coacting threadedelements having opposed ratchet teeth formed thereon and pressed intodriving engagement by a belleville washer supported on the assembly by aseparate fastener.

SUMMARY OF THE INVENTION The purpose of the invention is to provide aninexpensive torque limiting threaded fastener and, as an ancillaryfactor, to provide an inexpensive adapter which will convert an ordinarywrench into a torque limiting wrench.

The invention resides in the use of a socket element or driver, adaptedto be torqued by a conventional wrench, which surrounds and isresiliently interconnected with the normal torque applying surfaces of aconventional threaded fastener thus obviating the necessity offabricating a special nut or bolt. The socket element is supported inspaced telescopic relationship to the nut or bolthead by the resilientinterconnection and the spacing is sufficient to permit relativerotation between the ut or bolthead and socket when the applied torqueexceeds the bias of the resilient interconnection.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of a blank from whichthe driver or socket element may be fabricated;

FIG. 2 is a sectional view of the blank of FIG. 1 undergoing a first dieforming operation with an associated punch being fragmentarily shown inelevation;

FIG. 3 is a sectional view taken along line 3--3 of FIG. 2;

FIG. 4 is a perspective view illustrating the assembly of a conventionalnut with the finished driver;

FIG. 5 is an elevational view of the assembled torque limiting nutapplied to a bolt, and threaded down against a panel member;

FIG. 6 is a sectional view of the torque limiting nut and bolt takenalong the line 6-6 of FIG. 5 and illustrating, in phantom lines, theapplication of a torquing force to the nut;

FIG. 7 is a fragmentary plan view of a blank used to fabricate amodified torque limiting nut;

FIG. 8 is a partially broken plan view of a torque limiting nutemploying the blank of FIG. 7;

FIG. 9 is a sectional view of the driver taken along the line 99 of FIG.8 with the conventional nut being shown in elevation;

FIG. 10 is a plan view of a second embodiment employing a sleeveretainer to preclude disassembly of the torque limiting nut in a serviceenvironment; and

FIG. 11 is a sectional view taken along line 1 11l of FIG. 10 with theconventional nut being shown in elevation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention is hereinillustrated in conjunction with a conventional hex nut to exemplify theprinciples which are equally applicable to a bolthead or otherconventionally configured nut, such as one having twelve sides.

A spring metal blank 10, such as a high carbon steel or a hardenable 400series stainless steel, is shown in FIG. 1 wherein the solid linesindicate where a shearing operation will occur and the dotted linesrepresent bending lines. The blank 10 is placed on a die 12 overlyingrecesses 14 having a lower reentrant portion 16 adapted to coact withsimilarly formed punches 18 to form struck out resilient tangs orfingers 20 whose remote ends have one edge thereof turned upwardly atapproximately 45 to form a cam surface 22. The blank is then removedfrom the die and formed into a closed hexagonal shape as by bendingalong the dotted lines 24 shown in FIG. 1 and the opposed ends arerigidly secured to form the completed driver or socket element 26 havingcircumferentially continuous portions or driver means on either side ofthe struck out tangs. If the blank 10 was a hardenable material, it isnext hardened prior to assembly with a conventional hex nut 28 as by theforcible telescopic engagement of the two as indicated by the arrow 30in FIG. 4. The diameter of a circle whose circumference passes throughthe innermost ends of the unflexed fingers 20 prior to the assembly stepof FIG. 4 has a lesser diameter than the smallest diameter of hex nut28, i.e., a diameter which is perpendicular to one of the flat torqueapplying faces 32. Telescopic assembly of the hex nut and driver is madepossible by cam surfaces 22 which cams fingers 20 outwardly upon initialengagement withfthe corresponding edges of the flat hex nut surfaces 32.

The completed-assembly forming a torque limiting nut 34 is shown inFIGS. 5 and 6 wherein driver 26 exerts a strong frictional grip on threeof the hex nut surfaces 32 through the flexed spring fingers 20. Selftorquing nut 34 may be tightened by a conventional wrench 36 applied toopposed torque applying surfaces 38 on driver 26. It will be apparentthat torque applied to driver 26 will be transmitted to hex nut 28 untilsuch time as the applied torque exceeds the resilient bias of springfingers 20. When the applied torque which can be transmitted by springfingers 20 is exceeded, the findesired, by inserting a screwdriverbeneath the lower surface thereof and prising upwardly against a securedstructural member 40. i

The embodiment shown in FIGS. 7-9 differs from that previously describedin the provision of a plurality of discrete inturned projections 42 on adriver 44 forming a continuous flange 46 adapted to engage a pluralityof shallow grooves 48 machined at the angles of hex nut 50. Thisprovides a mechanical interlock between the driver and hex nutprecluding their disassembly at all times. The discrete projections 42forming the inturned flange 46 are sufficiently resilient to yieldslightly as the nut and driver are being assembled and then snap intothe shallow grooves 48.

The torque limiting nut shown in FIGS. and 11 retains the advantages ofthe first described embodiment utilizing a conventional nut that doesnot require any modification, such as the grooves 48 in the secondembodiment, while yet maintaining a positive interlocked assembly underservice conditions. Basically, a conventional nut 52 is telescopicallyassembled with a similarly configured, split retainer sleeve 54 whichfits snugly against the sides of the nut before the assembled nut andretainer are assembled with a driver 56 which is identical to the driver26 shown in FIG. 4. Retainer sleeve 54 need not be formed from springmaterial but may be made in the configuration shown in FIG. 11 in anydesired manner such as by casting, stamping or the like. Sleeve 54includes an inwardly turned flange 58 adapted to abut the lower surfaceof nut 52, as viewed in FIG. 11, whereby the same will be clampedbetween nut 52 and the structural member through which the associatedbolt will extend. The other end of the retainer sleeve is formed with anoutwardly turned flange 60 which will overlie spring fingers 62 when thedriver 56 is subsequently assembled with the nut and retainer sleeve.This latter assembly is effected in the same manner as that described inconnection with FIG. 4 with the hexagonal sides of retainer sleeve 54being pressed tightly against the corresponding sides of nut 52 by thebias of spring fingers 62. The diametrically opposed split lines 64extend through upper flange 60 and the sleeve body to terminate at thelevel of lower flange 58. The use of a split retainer sleeve permitsgreater manufacturing tolerances and allows the sleeve to flex slightlyunder the bias of spring fingers 62 to more snugly engage the sides ofnut 52. The sleeve retainer may be split at each corner, if desired, tofacilitate fabrication by stamping.

In operation, the completed torque limiting nut shown in FIGS. 10 and 11is threaded onto a bolt and as the torquing forces are increasedclamping flange 58 between nut 52 and a structural member, retainersleeve 54 acts as an integral part of nut 52 since it can not moverelative thereto. Thus, the driver acts in relation to the nut-retainercombination in the same manner as was described in connection with theembodiment shown in FIGS. 5 and 6. It will be apparent that driver 56cannot be removed from retainer sleeve 54 because of the flange 60overlying fingers 62.

In order to loosen the self torquing nuts shown in FIGS. 8, 9 and 10, 11which will normally require the I application of a substantially greateruntorquing force than was necessary to torque the same; the point of ascrewdriver may be inserted between the driver and nut of FIGS. 8 and 9or between the driver and retainer sleeve of FIGS. 10 and l l. Thescrewdriver thus serves as a solid abutment precluding relative rotationof the driver and substantial untorquing forces may thus be transmittedfrom the driver to the nut.

Alternatively, in the embodiment of FIGS. wand 11, raised protuberancescould be cast integrally with the outer hexagonal periphery of retainer64 just ahead of the remote ends of spring fingers 62, as viewed in acounter-clockwise direction, so that upon the application of anuntorquing force of sufficient magnitude to initiate relative rotationbetween the driver and retainer, the two would be positively coupled forcounter-clockwise rotation.

In an application of any of the three embodiments to a relatively smallthreaded fastener where the necessary width of spring fingers 20, 62 iswide in comparison to the width of the blank from which they are struckthus rendering the driver circumferentially weakened; a second solidcast driver may be tightly interfitted about any of the drivers 26, 44,54. Alternatively, in the case ofa low profile nut, thecircumferentially continuous portion of the driver may lie above thenut.

It is obvious that ifa self locking fastener is required, the driver maybe assembled with any of a plurality of conventional self locking nuts.Furthermore, in the event locking wires are required they may bethreaded through the openings left by the struck out spring fingers or,in the case of the FIG. 10 embodiment, locking wire holes could be castintegrally with flange 60.

I claim:

l. A torque limiting fastener, comprising; a rotatable threaded fastenerincluding a plurality of flat torque applying surfaces tangentiallydisposed to a common circle the center of which lies on the rotationalaxis of said fastener, circumferentially continuous driver meanscomprising a peripheral band having a like number of flat torqueapplying surfaces, relation to said flat torque applying surfaces ofsaid fastener in spaced concentric relationship thereto, and said torquetransmitting means including yieldable fingers struck from said band atthe corners thereof, whereby said driver means may rotate relative tosaid threaded fastener upon application of excessive torque.

2. The torque limiting fastener of claim 1 wherein said yieldable meansare in direct torque transmitting engagement with said flat torqueapplying surfaces.

3. The torque limiting fastener of claim 2 including means coactingbetween said driver and fastener for precluding relative movement in atleast one axial direction.

4. The torque limiting fastener of claim 1 wherein said torquetransmitting means further include retainer means non-rotatably mountedon said threaded fastener, and said yieldable means directly engagingsaid retainer means.

5. The torque limiting fastener of claim 4 wherein said retainer meansincludes an inwardly directed flange adapted to be clamped between saidfastener and a fastened structure, and an outwardly directed flange forprecluding substantial axial movement of said driver means relative tosaid threaded fastener.

6. A self torquing nut, comprising; a nut having conventional torqueapplying faces lying tangent to a common circle, circumferentiallycontinuous driver means comprising a peripheral band having a likenumber of said driver means exceeding all diameters of. said nut wherebythe driver may rotate relative to said nut upon the application ofexcessive torque. I 7. The self torquing nut of claim 6 including meansfor precluding movement of said driver means relative to said nut in atleast one axial direction.

1. A torque limiting fastener, comprising; a rotatable threaded fastenerincluding a plurality of flAt torque applying surfaces tangentiallydisposed to a common circle the center of which lies on the rotationalaxis of said fastener, circumferentially continuous driver meanscomprising a peripheral band having a like number of flat torqueapplying surfaces, relation to said flat torque applying surfaces ofsaid fastener in spaced concentric relationship thereto, and said torquetransmitting means including yieldable fingers struck from said band atthe corners thereof, whereby said driver means may rotate relative tosaid threaded fastener upon application of excessive torque.
 2. Thetorque limiting fastener of claim 1 wherein said yieldable means are indirect torque transmitting engagement with said flat torque applyingsurfaces.
 3. The torque limiting fastener of claim 2 including meanscoacting between said driver and fastener for precluding relativemovement in at least one axial direction.
 4. The torque limitingfastener of claim 1 wherein said torque transmitting means furtherinclude retainer means non-rotatably mounted on said threaded fastener,and said yieldable means directly engaging said retainer means.
 5. Thetorque limiting fastener of claim 4 wherein said retainer means includesan inwardly directed flange adapted to be clamped between said fastenerand a fastened structure, and an outwardly directed flange forprecluding substantial axial movement of said driver means relative tosaid threaded fastener.
 6. A self torquing nut, comprising; a nut havingconventional torque applying faces lying tangent to a common circle,circumferentially continuous driver means comprising a peripheral bandhaving a like number of flat torque applying surfaces, a plurality ofyieldable fingers struck from said band at the corners thereof andextending inwardly from said peripheral band for mounting said drivermeans in torque transmitting spaced telescopic relationship to said nut,said fingers including resilient means adapted to yield upon theexertion of a predetermined torque, and all diameters of said drivermeans exceeding all diameters of said nut whereby the driver may rotaterelative to said nut upon the application of excessive torque.
 7. Theself torquing nut of claim 6 including means for precluding movement ofsaid driver means relative to said nut in at least one axial direction.